1. Field of the Invention
The present invention relates generally to cooling towers and more particularly, but not by way of limitation, to an improved drainage collection system for a direct forced draft counterflow cooling tower.
2. Description of the Prior Art
One common type of industrial cooling tower is a counterflow tower wherein water falls downward through a fill layer while cooling air moves upward through the fill material. The term "counterflow" refers to the fact that the warm water and cool air are moving in opposite directions.
Counterflow cooling towers traditionally may be of three types, namely induced draft, natural draft, and forced draft.
An induced draft counterflow cooling tower has a fan located on top of the tower which sucks air up through the fill material. Air flows laterally along the ground surface adjacent the tower and once it is under the tower it turns ninety degrees and flows upward through the fill material, with this flow being induced by the fans on top of the tower which suck the air up through the tower. Examples of induced draft counterflow cooling towers are seen in U. S. Pat. Nos. 4,267,130 and 4,301,097, both to Curtis.
U.S. Pat. No. 4,521,350 to Lefevre, shows at FIG. 1 thereof a natural draft counterflow cooling tower. A natural draft cooling tower does not utilize a fan to assist the air flow, but instead relies upon the natural tendency of warmer air to flow upward. The natural draft cooling tower shown in U.S. Pat. No. 4,521,350 is the type commonly referred to as a hyperbolic natural draft cooling tower. The Lefevre patent shows the use of a drainage collection system below the fill material in the natural draft counterflow cooling tower thereshown.
U.S. Pat. Nos. 2,606,750 and 2,915,302 to Jacir show forced draft counterflow water cooling towers. Forced draft towers traditionally have a fan located on the side of the tower which blows air into a plenum chamber on the lower side of the tower. A plurality of vanes are used to turn the air ninety degrees to direct it upward through the tower. As used in the trade, the term "forced draft" is understood to refer to a system like that of Jacir having a fan on the side of the tower blowing into a lower plenum so that the air must then turn ninety degrees to flow upward through the tower.
A second common type of cooling tower is a cross flow tower. Cross flow cooling towers have the warm water falling downward through fill material while cooling air is drawn in horizontally at approximately ninety degrees to the path of the falling water. These cross flow cooling towers are typically induced draft towers which have a plenum chamber and fan located on top of the tower sucking the air up through the tower.
The prior art also includes a cross flow cooling tower having a fan located below the tower for forcing air upward into a central plenum chamber so that the air then turns ninety degrees and flows horizontally out through the fill material which is located around the perimeter of the tower. Such a system has been marketed by the Marley Cooling Tower Company. In that system, there is no fill material located directly above the fan, but rather the fill material is all located around the perimeter of the fan, with the area directly above the fan defining a plenum chamber into which the fan blows.
The prior art also includes many versions of drainage collection systems made up of a series of overlapping sloped collection plates with troughs along their lower edge. Such a system is shown for example in the Lafevre U.S. Pat. No. 4,521,350 patent cited above.
Industrial cooling towers typically are very large structures having lateral dimensions on the order of twenty to one hundred feet and having a height on the order of twenty to thirty feet. Such structures are built at the field site. Typical delay between the time of order and the time of completion of an industrial cooling tower is on the order of one year. The construction of such a tower is a major undertaking.
Although relatively small towers have been built which could be transported to the field site, for example, some rooftop towers used for the mechanical systems of office buildings and the like, until recently there has not been a successful modular cooling tower system whereby individual modules of a size that can be readily transported are fabricated in a factory, and then easily assembled at a field site to provide the large capacity demanded by many industrial water cooling projects. Such a modular system has recently been introduced by the assignee of the present invention and is shown and described in U.S. Pat. No. 5,227,095 to Curtis, the details of which are incorporated herein by reference. The system of the Curtis '095 patent has the fan located below the fill for forcing air directly upward through the fill; this may be referred to as a direct forced draft counterflow cooling tower. Applicant hereby acknowledges that structures substantially like those shown in the Curtis '095 patent have been on sale for more than one year prior to the filing of the present application, and thus the subject matter described in the Curtis '095 patent is prior art to the present application.